1. Field of the Invention
The present invention relates to a plasma processing apparatus and, more particularly, to a plasma processing apparatus which is suitable for etching a workpiece, such as a semiconductor element substrate, by using plasma and applying a high frequency voltage to the substrate.
2. Description of the Related Art
In conventional plasma processing apparatus, for example, as described in Patent Document 1, a high frequency voltage having a sine waveform was applied to an electrode on which a wafer, which is the object to be processed, is placed. In this case, as shown in FIG. 12, the ion energy distribution on the wafer has a saddle peak distribution which has two peaks, one on the high energy side and one on the low energy side. Although ions of the high energy peak contribute to etching, ions of the low energy peak scarcely contribute to etching. In a case where a high frequency voltage having a sine waveform is applied, the ratio of the high energy peak height to the low energy peak height is almost 1:1. Even when the high frequency voltage is changed, this high/low energy ion ratio scarcely changes, posing the problem that the etching efficiency is low.
Patent Document 1: Japanese Patent Laid-Open No. 5-174995
The object of the present invention is to provide a plasma processing apparatus capable of high etching rate and high performance etching.